1. Field of the Invention
This invention relates to a beam splitting device and more particularly to a beam splitting device in which the light beam from an objective lens is split by a beam splitter and an optical path length difference is imparted to at least one of the optical paths of the split light beams, so that at least two images having an optical path length difference are formed on a plurality of rows or sensors disposed substantially on the same plane, whereby these images are detected.
2. Description of the Prior Art
A device of the described type is applicable to a focus detecting system for a camera. As the means for splitting the light beam from the objective lens of this reading apparatus, the assignee of the subject application has already proposed an area-type beam splitter in Japanese patent application No. 98524/1980 filed on July 17, 1980 corresponding to U.S. patent application Ser. No. 283,001 filed on July 13, 1981. In this prior application, there is disclosed, as an example of the area-type beam splitter, a beam splitter comprising dot-like or stripe-like minute reflecting mirrors deposited on a glass substrate by evaporation and effecting beam splitting by reflection and transmission.
However, these beam splitter, which comprises minute reflecting mirrors deposited on a glass substrate by evaporation, is costly and difficult to manufacture.